Colorants are used in most consumer products to provide a distinctive and pleasing appearance. Food and personal care products use almost exclusively two kinds of colorants: Food, Drug and Cosmetic (xe2x80x9cFDandCxe2x80x9d) dyes and Drug and Cosmetic (xe2x80x9cDandCxe2x80x9d) dyes, because both kinds of these dyes are non-toxic. In addition to their non-toxicity, these dyes have the additional benefit of being water-soluble, and so when admixed into an aqueous consumer product they are homogeneously distributed throughout the bulk of the product to give it a uniform color.
However, these dyes may not be suitable for use in a multi-colored consumer product. Multi-colored consumer products are those that have two or more regions of contrasting color and/or consistency. Examples of multicolored products are toothpastes that are transparent or white and contain small speckles, as well as toothpastes made from two or more layers, each having its own distinctive color.
While multi-colored consumer products may be more attractive to consumers, they pose difficulties in formulation and manufacture. In particular, such products are susceptible to the effects of dye migration between the differently colored regions. xe2x80x9cDye migrationxe2x80x9d in this sense refers to the tendency of a dye in a multilayered product to migrate from one region of a product into an adjacent region of a product. Such migration occurs by the physical process of diffusion and is also known as xe2x80x9cbleedingxe2x80x9d. This migration or bleeding is undesirable because it compromises the distinctive appearance of the consumer product and prevents the product formulator from predictably controlling the aesthetics of the product.
One way to prevent dye migration is to physically separate the differently colored regions until actual use. For example, toothpaste containers have been developed for storing multi-layered toothpastes that maintain each of the layers in a separate compartment until the layers are combined as a single toothpaste product upon dispensing from the container. While this mechanical approach to the problem of dye migration is effective, such containers are expensive and increase the cost of the product.
Using alternative colorants instead of FDandC and DandC dyes may provide a chemical solution to the problem of dye migration that is considerably less expensive than the aforementioned mechanical solution. Colored pigments, which are finely powdered, water-insoluble materials that are dispersed and suspended in a consumer product are one possible alternative to the water-soluble dyes. Indeed, because they are water-insoluble these pigments are highly resistant to dye migration in aqueous compositions.
Unfortunately, most conventional colored pigments are not suitable for use in food or personal care products because of concerns relating to their toxicity. But these toxicity concerns may be managed by substituting xe2x80x9clake pigmentsxe2x80x9d for conventional pigments. Lake pigments are colorants formed by reacting an organic dye with aluminum or calcium salt on a water-insoluble inorganic substrate. The most commonly used substrate is alumina. Lake pigments can be manufactured to be non-toxic and suitable for use in food, drugs and personal care products. However, while lake pigments are more resistant to dye migration than FDandC and DandC dyes, they still exhibit an unacceptably high level of dye migration.
Given the foregoing, there is a continuing need to develop non-toxic colorants that are both non-toxic and highly resistant to dye migration so as to make them suitable as colorant additives in multi-colored consumer products.
The invention includes a method of forming a calcium phosphate colorant. A first step of this method is providing a calcium phosphate slurry comprising calcium phosphate particles. Aluminum hydroxide is mixed with the calcium phosphate slurry to form a premix, thereby depositing aluminum hydroxide onto the calcium phosphate particles. Thereafter, a dye is added to the calcium phosphate particles having been treated with aluminum hydroxide, wherein the dye is fixed to the calcium phosphate particles by the aluminum hydroxide.
The invention also includes a calcium phosphate colorant resistant to dye migration and comprising calcium phosphate particles, a dye, and aluminum hydroxide.
Preferred dyes include FDandC and DandC dyes.
All parts, percentages and ratios used herein are expressed by weight unless otherwise specified. All documents cited herein are incorporated by reference.
The following describes preferred embodiments of the present invention, which provides calcium phosphate colorants as well as a process for making such colorants. These colorants are suitable for use in cosmetic, food, and oral care products having excellent resistance to dye migration and being non-toxic.
By xe2x80x9cmixturexe2x80x9d it is meant any combination of two or more substances, in the form of, for example without intending to be limiting, a heterogeneous mixture, a suspension, a solution, a sol, a gel, a dispersion, or an emulsion.
By xe2x80x9ccoatedxe2x80x9d it is meant that the specified coating ingredient covers at least a portion of the outer surface of a particle or substrate.
By xe2x80x9cslurryxe2x80x9d it is meant an aqueous mixture of water and at least one other component, wherein water forms the continuous phase.
By xe2x80x9ccosmetic productxe2x80x9d it is meant any product applied directly to an external or internal part of the body, for example without intending to be limiting, make-up, eye shadow, foundations, lipstick, nail polish, aftershaves, facial creams, shower gels, toothpastes, clown make-up, novelty Halloween costume creams and make-up, sensory perception agents, shaving cream, shampoos, bar soaps, liquid soaps, detergents, foot powders, anti-perspirants and deodorants, eye liners, body glitter, theatrical make-up, body paints, and moisturizers.
By xe2x80x9cdentifricesxe2x80x9d it is meant oral care products such as, without intending to be limiting, toothpastes, tooth powders and denture creams.
By xe2x80x9cfood productxe2x80x9d it is meant any product meant to be consumed, as well as additives to food products such as, without intending to be limiting, food colorants, anti-caking and free flow agents.
By xe2x80x9cdyexe2x80x9d it is meant an organic colorant, derived from coal tar and petroleum-based intermediates.
By xe2x80x9ccolorantxe2x80x9d it is meant any substance that imparts color to another material or mixture.
By xe2x80x9clake pigmentxe2x80x9d it is meant a colorant made by extending on an alumina substrate, a salt prepared from water-soluble straight colors by combining such color with the basic radical aluminum or calcium.
By xe2x80x9cFandDC dyesxe2x80x9d and xe2x80x9cDandC dyesxe2x80x9d it is meant any dye listed in Title 21, part 82 of the Code of Federal Regulations, the content of which is hereby incorporated by reference.
By xe2x80x9cfixingxe2x80x9d is meant to hold a dye permanently on a substrate by chemical or mechanical action, or a combination of both.
The ingredients of the calcium phosphate colorant as well as a method for making the colorant will now be discussed in detail. Subsequently, products that comprise the calcium phosphate colorant will be discussed and examples of such products provided.
The present calcium phosphate colorant contains calcium phosphate, aluminum hydroxide and a dye.
The calcium phosphate is present as particles and these particles may be formed from a variety of suitable calcium phosphate species such as monocalcium phosphate, also known as monobasic calcium phosphate, acid calcium phosphate, calcium biphosphate, primary calcium phosphate and CaH4 (PO4)2; dicalcium phosphate, also known as dibasic calcium phosphate, calcium monohydrogen phosphate, secondary calcium phosphate and CaHPO4; dicalcium phosphate dihydrate, CaHPO4xc2x72H2O; tricalcium phosphate, which is also referred to by the following names: tribasic calcium phosphate, tertiary calcium phosphate, bone ash, TCP and Ca3(PO4)2; calcium pyrophosphate, also referred to as calcium diphosphate and Ca2P2O7. Preferred calcium phosphate species are tricalcium phosphate, Ca3(PO4)2, dicalcium phosphate, CaHPO4, and calcium pyrophosphate. The properties of these preferred calcium phosphate species are as follows:
In Table I, oil absorption was determined by the rub-out method of ASTM-D281. The pore volume was determined by mercury intrusion porosimetry using a micromeritics AutoPore II 9220 unit. Pore voumes were determined over an intrusion pressure range of 10.0 to 6,029 psi. Data were collected using an advancing contact angle of 130 degrees and a pressure equilibration time of 10 seconds per intrusion measurement point. The BET surface area was determined by the BET nitrogen absoprtion method of Brunaur et al., as reported in the J. Am. Chem. Soc. 60, 309 (1938). The particle size measures were made using a Leeds and Northrup Microtrac II apparatus. All of these tests are described in greater detail in U.S. Pat. No. 6,171,384, issued Jan. 9, 2001 to Conley et al.
The calcium phosphate particles are coated with aluminum hydroxide and dye. Methods for preparing the aluminum hydroxide are discussed below. Any water-soluble, non-toxic dye capable of forming a lake pigment can be used, while Food, Drug and Cosmetic (FDandC) or Drug and Cosmetic (DandC) dyes are preferred. Multiple dyes can be blended together so that by mixing together dyes of different colors a wide variety of colors can be obtained. For example, a green dye can be produced by mixing together blue and yellow dyes.
The process to combine the aforementioned ingredients to form a calcium phosphate colorant will now be discussed in greater detail.
First, a calcium phosphate slurry containing calcium phosphate particles is prepared. Next, the calcium phosphate is xe2x80x9ctreatedxe2x80x9d with aluminum hydroxide. The aluminum hydroxide, preferably in the form of a gel, may be prepared in advance and is deposited onto the calcium phosphate particles by mixing the aluminum hydroxide with the calcium phosphate slurry in a reactor or mixing vessel. Because it is desired to maintain a low concentration of Na2SO4 in the aluminum hydroxide, and because the conductivity of the aluminum hydroxide is proportional to the Na2SO4 concentration, the conductivity of the aluminum hydroxide gel should be adjusted to be less than 5000 xcexcmhos. If desired, instead of adjusting the conductivity of the aluminum hydroxide gel, the conductivity of the mixture of the calcium phosphate and aluminum hydroxide may be adjusted in the reactor vessel instead.
Alternatively, instead of preparing the aluminum hydroxide in advance, the aluminum hydroxide may be prepared in situ in the reaction vessel. The in situ method proceeds as follows. An aqueous solution of aluminum sulfate is first added to a reactor or mixing vessel, before any other chemical compounds. Then an aqueous solution of a base, preferably sodium carbonate, is added to the vessel and mixed with the aqueous solution of aluminum sulfate. The aluminum sulfate and base react to produce aluminum hydroxide according to the following reaction:
Al2(SO4)3+3Na2CO3+3H2Oxe2x86x923CO2+2Al(OH)3+3Na2SO4
Calcium phosphate slurry (comprising calcium phosphate particles) is then added to the vessel and mixed together under agitation with the aluminum hydroxide, so that the calcium phosphate particles are coated with aluminum hydroxide. The resulting slurry is filtered and washed to remove by-product sodium sulfate and the wetcake thereby obtained is reslurried.
Subsequently, the calcium phosphate slurry prepared by either of the above described methods, or in fact any other suitable method, is colored by the addition of one or more dyes. The slurry of colored calcium phosphate is then filtered and dried at a temperature T1, to obtain a colored calcium phosphate having a moisture level M1; preferably M1 is less than about 10%, by weight. Conventional oven or spray-drying techniques are suitable. The colored calcium phosphate is then washed and filtered to remove excess dye, which continues until a colorless filtrate is obtained. The filtrate is considered colorless when it has an absorption of less than 0.1 at the wavelength that is characteristic of the dye as determined by UV/Visible spectrometry.
After the excess dye is removed, the wetcake produced by the combination of washing and filtering is dried at a temperature T2, to form a calcium phosphate colorant having a moisture level M2. It is important that the second calcium phosphate cake should never be dried to a moisture level lower than the moisture level of the first calcium phosphate cake (i.e., M2xe2x89xa7M1), and it is equally important that the temperature at which the second calcium phosphate cake is dried should always be less than the drying temperature of the first calcium phosphate cake (i.e., T1xe2x89xa7T2).
This calcium phosphate colorant is a lake pigment with the dye or dyes being xe2x80x9cfixedxe2x80x9d to the aluminum hydroxide coated calcium phosphate particles. Because of this fixing, the dyes strongly adhere to the particles and are therefore highly resistant against separating from the particles and contributing to dye migration
Having been formed from the aforementioned ingredients and by the aforementioned process steps, the present calcium phosphate colorants may be used in a variety of different consumer products, such as cosmetic products, dentrifices and food products. Specifically, if the calcium phosphate colorant is to be used as the colorant in a layer of a striped toothpaste (as discussed in greater detail below), then after drying the colorant should be preferably milled to a powder, i.e. to a median particle size of less than 25 xcexcm and preferably from about 5 xcexcm to about 15 xcexcm (as measured with a Horiba particle size analyzer). If the colorant is used instead to form speckles in a toothpaste formulation, it is compacted into granules and the granules screened to a size of about 600 xcexcm to about 180 xcexcm.